Apparatus and process for desliming flotation feeds



Aug. 18, 1942.

H. 1.. MEAD ETAL 2,293,033 APIARA'I'US AND rnocnss For: mzsnnqne momnon FEED Filed April 5, 1940 2 Sheets-Sheet 1 INVENTORS law/FRY 4 M540 LOP/V4197 u. M4057 ATTORNEY.

Aug. 18, 1942. I

H. L. MEAD EI'AL 2,293,033. APPARATUS AND PROCESS FOR DESLIMING FLOI'ATION FEED Filed April 5, 1940 Z-Sheets-Sheet 2 INVENTORS' H4??? A M6 40 ATTORNEY.

v Patented Aug. '18, 19 42,

APPARATUS AND rnocsss FOR nasrmmo morarron mans Barry L. Mead and Ernest J. Maust, Brewster,

Fla., assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine Application April 5, 1940, Serial No. 327,948

' 6 Claims. (c l. 209-454) This invention relates to the desliming of flotation feed in the ore dressing art and more particularly it relates to an improved apparatus of the hindered settling type for desliming the finest fraction of flotation feed.

Recent improvements in the flotation art have required that flotation feeds be very thoroughly deslimed,v that is to say, more completely than the desliming produced in the use of free settling tanks. This is particularly true in connection with the flotation of silica from phosphate rock using the so-called cationic flotation reagents as even very small quantities of slimehave a deleterious effect on the promoter action of the reagents.

In our copending application Serial No. 320,121 filed February 21, 1940, we have described an improved process for the simultaneous sizing and desliming of phosphate ore flotation feed in a hindered settling classifier, which is a much more eiiicient method than the ordinarily employed desliming, operations, the process, however, deals only with the desliming of the larger particlefractions of the phosphate material and does not result in slime removal from the very fine fraction of phosphate material to which the present invention relates.

The ordinary'methods of desliming very'fine flotation feed in the past have ,not been found to be entirely satisfactory. The prior methods of desliming very flne ore material usually consists of passing the material into a series of large settling tanks with the addition of large volumes of fresh water to each of the series of settling tanks. Adequate settling area in this case must be provided in each tank to settle all of the plus 250 mesh material each time that it enters a tank. As some. slime always tends to settle with true particle size material, the amount .of slimesettling in each tank of a series is a decreasing amount, but is never entirely removed as mathematically this is impossible. Hence, in previous methods it was not economically practical to obtain the high degree of desliming that is attained in the hydraulic hindered settling deslimer of this invention. The settling tanks of the prior methods might be cylindrical tanks with fiat bottoms, conical tanks, or rectangular tanks with bowl attachments wherein the settled material was raked out of-the bath.

In accordance with the present invention a process is provided in which very flne fractions of flotation feed can be thoroughly deslimed. An improved apparatus of the hindered settling type is provided in which the entire desliming opera operation.

tion is conducted in one tank where a small amount of water and a small area' does work equivalent to that accomplished by a series of large settling tanks employing much larger quantities of water. This improved apparatus is usefulior desliming very fine flotation feed of any ore material but it is particularly useful in the non-metallic field, especially the flnest fraction of phosphate flotation feed ranging from -48 mesh down to 325 mesh.

In carrying out our invention use is made of the density of a teetering mass of fine flotation feed to keep the light slime from-entering the denser body of material in suspension. A density in excess of that of water is induced in the pockets of the hindered settling deslimer due to the particles being held in teeter by means of the hydraulic water passing through the constriction plate in the bottom of the compartment. Hence, in addition to the tendency for a rising column of water to carry off slime, the density of the material in suspension also tends to aid in slime removal. In our improved bindered settling deslimer water is added at such a rate that only about 6 gallons per minute per square foot of overflow area is used. In the ordinary hindered settling classifier water in excess of this amount must be used to keep the particles in suspension and thus fine flotation feed-is overflowed. This water limitation at a point of not over about 6 gallonsper minute per square foot of overflow area is made possible and teeter still maintained by flaring the hydraulic chamber at a point above the teeter column.

It is an advantage of the present invention that the finest fraction of phosphate flotation feed which cannot be deslimed in the ordinary hindered settling classifier (-48 mesh down to 325 mesh) is readily deslimed using our improved apparatus. A very thoroughly deslimed product is produced, which deslimed feed when subjected to froth flotation concentration by either the silica flotation process or the fatty acid phosphate flotation process results in a higher grade product and The present invention has many advantages over the prior desliming processes such as those using a series. of settling tanks or cones, drag classifiers and the like. Some of these outstanding advantages are low first cost of equipment, small floor space. and economy of about to in the use of water over the free settling desliming. When compared to a desliming process using a series .of these cones it was found permits more efllcient same time the initial cost was only about as much to produce a better deslimed product.

,The invention will be more readilyunderstood by referring to the following drawings of our improved hindered settling deslimer apparatus in which:

Fig. 1 is a longitudinal sectional view;

Fig. 2 isv a top plan view; and

Fig. 3 is a transverse sectional view taken along the lines 3-3 of Figs. 1 and 2 and looking in the direction of the arrows.

The deslimer comprises atank I having the flaring sides 2. The lower half 01' the tank is divided into a plurality of pockets or compartments as illustrated. These pockets are numbered from I to I3 inclusive. A hydraulic water compartment 3 is located beneath the pockets and separated therefrom by the perforated constriction plate 4 through which hydraulic water may be flowed. Any number of pockets may be used, the number being optional and limited only to a practical size over which water may be uniformly distributed through'the holes of the constriction plate in the hydraulic water compartment 3. Hydraulic water inlets 22 are shown leading into the various portions of the hydraulic water compartments 3 in such a manner that varying amounts of water and at different velocities may be forced through the constriction plate 6 into each oi the pockets I to I3 inclusive. A baiile plate I4 divides each of the pockets from the adjoining pockets from I to I2 inclusive. All

of the pockets except I3 are connected through a suitable opening or slot I5 in the battles I4. While the slot I5 is shown extending only part way up the bafiles I4, it may, if desired, be extended to the top. A standpipe I1 is shown positioned in the pocket I2, in such a manner that changes of specific gravity in this compartment cause water to rise in the pipe actuating a diaphragm 20 operatively connected to the top of the standpipe. This diaphragm may be 'of the ordinary flexible rubber type but is preferably a bellows diaphragm. When the diaphragm is forced upwardly by water pressure the plumb bob valve I8 which is seated in the discharge opening IS in the bottom of pocket I3 is raised a sufiicient height to permit the deslimed feed to pass out through the opening I9. Each of the pockets I to I3 inclusive may for convenience have observation windows 23 which will permit the operator to view the passage of the feed through these compartments. A feed opening 2I is so arranged in conjunction with the baffle I6 that when feed is introduced it passes directly into the compartment 1. An overflow area at the top of the flared portion of tank 2 is provided by means of the weir 5 by which water and slime are overflowed into the overflow launder 6. The weir 2| prevents overflow at the most distant portion of the tank from the feed entrance.

In operation a very fine flotation feed, as for example in the case of phosphaterock ranging in particle size from 48 to 325 mesh, is fed into the feed opening 2I and thence into th compartment I, whereupon the rising currents of hydraulic water passing through the construction plate .4 carry the flner slime particles into the flared portion of the tank. Here the upward velocity of the water decreases due to the increased area. The velocity is, however, sumcient to carry the slimy Particles over the weir 5.

The velocity of the water in the flared portion of the tank is not sufficient, however, to support the ore particles and they fall back into the pockets. The feed passes from the pocket I into the pocket 8 by means of the slot I5 and ishere subjected to hydraulic water at a velocity diflerent from that in pocket I. This process is repeated as the feed passes from pocket to pocket, additional quantities of slime being removed in each pocket until the thoroughly deslimed feed collects in the last pocket I3, from which it is subsequently discharged by operation of the diaphragm actuated through the changes of speciflc gravity in pocket I2 to open the plumb bob valve seated in the feed discharge opening I9. There is no opening in the baflle I4 separating pocket I2 from pocket I3 and the velocity of the hydraulic water in I3 is just enough less than that of pocket I2 so that the feed passing over the top of baille It into pocket I3 will settle or.

collect at the bottom.

We have found that a very fine fraction of phosphate flotation feed can be very thoroughly deslimed in accordance with the above operation, by which even the 250 mesh material may be retained using an apparatus in which approximately 2000 gallons per minute for 50 long tons per hour of feed were being processed. Amon the important features which appear to be in a general measure responsible for the improved results of this apparatus are the flared sides of the tank which increase the area and reduce the velocity of the uprising currents of water so that the slimes are carried over the top and the ore materials fall back and can be collected.

By restricting the overflow at a point where the material is to be removed, we provide a positive flow of a small amount of remaining slime in a direction opposite to that of the passage of feed. This is an important part of the invention. Another important part of this invention is the restricting of the flow rate of waterin the cell in which the material is discharged to a point low enough to settle all 01 the plus 250 mesh flotation feed. As water is added in excess of this amount in the other cells, limiting the velocity of upward flow to a point below 6 gallons per minute per square foot of overflow area at the overflow point, the finest of the flotation feed could not settle into the bottom of these pockets to be discharged. Hence, in the pocket through which the material is discharged the velocity of the rising current of water is maintained at a point below 6 gallons per minute per square foot of area. As the flne material is not agitated sufflciently at this low flow rate to actuate a diaphragm discharge mechanism, this mechanism is operated from the superelevation water in the adjoining pocket to discharge the deslimedfeed in the discharge compartment.

In a preferred embodiment of our apparatus a diaphragm actuated device working through superelevation of the material in teeter in a pocket of the machine to discharge the material, from an adjoining pocket is employed. The deslimed feed might also be discharged by means of a hand operated valve, a centrifugal pump or a simple spigot, without violating the basic features of the invention. ,There are many advantages however, which result from the use of the teeter column .actuated diaphragm pump,

type of feed, amount of feed or other operating conditions.

In utilizing our improved apparatus no sizing is attempted unless we differentiate between colloidal slime and true particle size of about250 mesh. The rising velocity of the hydraulic water is regulated in such a manner that it is sufiicient to float away the colloidal slimes while at the same time it is approximately equal .to or less than the free settling rate of 250 mesh sand. When the velocity of the rising water is thus regulated the 260 mesh sand and, ofcourse, the material larger than 250 mesh readily separates out and is completely free from the colloidal slimes.

We claim:

1. A-method of desllming withoutclassifying slimy ore feed containing fine particle sizes which comprises introducing the feed into a rising column of water the velocity of said rising column being such as to cause the coarsest particles of the feed to remain in suspension, subjecting said stream of water to deceleration to a velocity at which the finest ore particles settle but slime rises, overflowing a portion of the water at said velocity to remove slime, causing said deslimed materials to pass into a zone of rising water the velocity of whichis such that the particles just settle in a discharge zone and discharging the settled ore particles from said discharge zone at a rate determined by sensing means located in a zone 'preceding the discharge zone. a

2. A method of desliming without classifying slimy phosphate ore feed containing very flne particle sizes, which comprises introducing the feed into a rising column of water the velocity of said rising column being such to cause the coarsest particles of the feed to remain in suspension, subjecting said stream of water to deceleration to a velocity at which the finest ore particles settle but slime rises, overflowing a portion of the water at said velocity to remove slime, causing said deslimedmaterial to pass into a zone of rising water the velocity of which is such that the finest ore particles just settle in a discharge zone and discharging the settled ore particles from said discharge zone at a rate determined by sensing means located in a zone preceding the discharge zone.

3. A method of desliming without classifying slimy phosphate ore feed containing very fine particle sizes, ranging from -48 to+325 mesh which comprises introducing the feed into a rising column of water the velocity of said rising column being such to cause the coarsest particles of the feed to remain in suspension, subjecting v said stream of water to decelartion to a'velocity at whichthe finest ore particles settle but slime rises, overflowing a porion of the water at said velocity to remove slime, causing said deslimed material to pass into a zone of rising water the velocity of which is such that the finest ore, 250

4. A hind red settling deslimer comprising a which tank-the upper portion of which has flared sides and an overflow area for slimes, a series of feed water in order to overflow from the tank,

said pockets in the series communicating with one another through restricted openings in the sides thereof with the exception that there is no communicating opening in the wall of the discharge pocket and the preceding'pocket.

5. A hindered settling deslimer comprising a tank the upper portion of which has flared sides and, an overflow area for slimes,'a series of pockets located in the lower portion of the tank and having perforated bottoms, means for introducing ore material into one of the pockets, means for discharging the coarser ore material in a pocket located at the opposite end of the series from the one into which the feed is introduced, means for introducing water through the aforesaid perforated bottoms into each of the pockets at a variable velocity, means for restricting overflow above the pocket from which the deslimedieed is discharged which causes the excess water to fiow in a direction opposite to that of the passage of feed water in order to overflow from the tank, said pockets in the series communicating. with one another through restricted openings in the sides thereof with the exception that there is no communicating open-- ing in the wall of the discharge pocket and the' preceding pocket.

6. A hindered settling deslimer comprising a tank the upper portion of which has flared sides and an overflow area for slimes, a series of pockets located in the lower portion of the tank and having perforated bottoms, means for introducing ore material into one of the pockets, means fordischarging the coarser ore material comprises a diaphragm mechanism actuated by density changes in one pocket to operate a feed discharge opening in the bottom ot another pocket located at the opposite end of the series from the one into which the feed is introduced, means for introducing water through the aforesaid perforated bottoms into each of the pockets at a variable velocity, means for restricting overflow above the pocket from which the deslimed feed is discharged which causes the excess water to flow in a direction opposite to that of the passage of feed water in order to overflow from the tank, said pockets in the series communicating with one another vthrough restricted openings in the sides thereof with the exception that there is no communicating opening in the wall of the discharge pocket and the preceding pocket.

. HARRY L. MEAD.

ERNEST J. MAUST. 

